The present invention relates to a plasma processing apparatus and plasma generation method.
More specifically, the present invention relates to a plasma processing apparatus and plasma generation method which generate a plasma by an electromagnetic field supplied into a processing vessel using a slot antenna.
The present invention also relates to a plasma processing apparatus and plasma generation method which generate a plasma by using electrons heated by electron-cyclotron-resonance (ECR).
In the manufacture of a semiconductor device or flat panel display, plasma processing apparatuses are used often to perform processes such as formation of an oxide film, crystal growth of a semiconductor layer, etching, and ashing. Among the plasma processing apparatuses, a high-frequency plasma processing apparatus is available which supplies a high-frequency electromagnetic field into a processing vessel by using a slot antenna and ionizes and dissociates a gas in the processing vessel by the operation of the electromagnetic field, thus generating a plasma. The high-frequency plasma processing apparatus can perform a plasma process efficiently since it can generate a low-pressure, high-density plasma.
According to one scheme of the high-frequency plasma processing apparatus, circular polarization feeding is performed through a cylindrical waveguide into a waveguide having a slot antenna. A circularly polarized wave is an electromagnetic wave the electric field vector of which forms a rotating electric field that rotates by one revolution in one period in a plane perpendicular to its traveling direction. When circular polarization feeding is performed, the distribution of the electric field in the waveguide having the slot antenna becomes axi-symmetric about the axis of the traveling direction of the circular polarization on the time average. Hence, a high-frequency electromagnetic field with an axi-symmetric distribution on the time average can be supplied into the processing vessel through the slot antenna, so that a uniform plasma can be generated by the operation of the electromagnetic field.
FIG. 15 shows the conventional arrangement of the power feed unit of a plasma processing apparatus which employs the circular polarization feeding scheme. The power feed unit feeds a circularly polarized wave to a radial line slot antenna (to be abbreviated as RLSA hereinafter) 530 as one type of a slot antenna, and has a high-frequency generator 543 which generates a high-frequency electromagnetic field, a rectangular waveguide 542 with one end connected to the high-frequency generator 543, a rectangular cylindrical converter 592 with one end connected to the other end of the rectangular waveguide 542, a cylindrical waveguide 541 with one end connected to the other end of the rectangular cylindrical converter 592 and the other end that opens to the interior of the RLSA 530, and a circular polarization converter 591 arranged in the cylindrical waveguide 541.
As the circular polarization converter 591, one as shown in FIG. 16A is used which is formed by arranging one or a plurality of pairs of cylindrical metal stubs 591A and 591B on the inner wall of the cylindrical waveguide 541 to oppose each other. The stubs 591A and 591B which form a pair are arranged in directions that form angles of 45° with the main direction of the electric field of the TE11-mode high-frequency electromagnetic field input from the rectangular cylindrical converter 592. When a plurality of pairs of stubs 591A and 591B are provided, they are arranged at an angular interval of λg/4 (where λg is the tube wavelength of the cylindrical waveguide 541) in the axial direction of the cylindrical waveguide 541, and convert the TE11-mode high-frequency electromagnetic field into a rotating electromagnetic field the main direction of the electric field of which rotates about the axis of the cylindrical waveguide 541 as the center.
As the circular polarization converter 591, one as shown in FIG. 16B is used in which one or a plurality of dielectric rods 591C are arranged perpendicularly to the axis of the cylindrical waveguide 541. The dielectric rod 591C is also arranged in the same direction as the main direction of the electric field of the TE11-mode high-frequency electromagnetic field input from the rectangular cylindrical converter 592 and at the same angular interval as that of the stubs 591A and 591B in the axial direction of the cylindrical waveguide 541, and converts the TE11-mode high-frequency electromagnetic field into a rotating electromagnetic field.
When large power is supplied, in the circular polarization converter 591 which uses the metal stubs 591A and 591B shown in FIG. 16A, the electric field focuses on the distal ends of the stubs 591A and 591B. Then, abnormal discharge tends to occur, and the operation of the plasma processing apparatus after discharge does not stabilize.
In the circular polarization converter 591 which uses the dielectric rod 591C shown in FIG. 16B, as the circular polarization converter 591 tends to be broken by heat generated by the dielectric rod 591C, it cannot withstand a continuous operation for a long period of time.
These problems occur when the circular polarization converter 591 is arranged in the cylindrical waveguide 541. Accordingly, these problem similarly occur in not only the high-frequency plasma processing apparatus described above but also an ECR plasma processing apparatus which feeds circular polarization into a processing vessel.